Adjustable cap for column foundation

ABSTRACT

A cap for a column-type foundation is adjustable with respect to its foundation. A top member has a support member for mating with and securing a leg of a structure and a central aperture for receiving an anchor rod of the column-type foundation. A sidewall casing extends downwardly from the top member and at least three positioning members engage the foundation. A seal is located on an inside of the sidewall casing near a bottom of the sidewall casing. The cap is filled with a settable material when connected to the foundation.

This application claims priority of U.S. provisional patent application 62/723,091 filed Aug. 27, 2018, and is incorporated herein by reference.

TECHNICAL FIELD

The present patent application relates to electrical power transmission and to foundation installation and construction for supporting towers and other structures.

BACKGROUND

Electrical power transmission lines are an important part of an electrical power grid infrastructure. Commonly, a tower is erected to support a transmission line. Some towers have a single central foundation support and use guy cables to stabilize the tower structure. These foundations support a downward load only. Other towers have multiple legs connected to foundation supports. These towers support the load of the downward weight of the tower, while also anchoring the tower when wind forces would cause one leg to want to lift or when the transmission lines terminate and/or change direction. In this latter type of tower, guy cables are not required.

The foundations for electrical power transmission line towers are typically directly built on the bedrock to ensure the desired stability when the bedrock is readily accessible (less than 5 meters deep). As illustrated in FIG. 1, this can involve the excavation of very large pit for each leg's foundation. The pit can extend down to the bedrock on which a foundation is built that extends up to ground level to support the leg of the tower. Rainfall and groundwater can fill the pits while installing the foundations and the environment is disturbed by the excavation. In cold climates, such foundation work must be done while protecting concrete from the cold while it sets. When conditions are difficult, the installation of a single tower for a 735 kV AC transmission tower as shown in

FIG. 1 can involve a cost of about $250,000 and to up to $500,000 when conditions are challenging (Canadian funds).

In many cases, the structure of the electrical transmission tower is based on angle iron members. The connection of each tower leg at the foundation typically involves connecting the leg to the foundation using strapping or other members that hold the legs down under tension so that wind forces cannot lift the legs.

Applicant has installed in Québec foundations for electrical transmission towers of a different nature than that illustrated in FIG. 1. These foundations, as illustrated in FIG. 2, avoid excavation down to the bedrock and instead rely on drilling a large borehole of about between 30 cm to 60 cm in diameter that extend through 2 m to 5 m of earth (i.e. the overburden layer 2) to reach the bedrock and then about 1 m to 2 m into the bedrock 3 for stabilization. These boreholes can be fitted with a sleeve 12 and are filled with a cement material 20 that then provide rigid support columns providing an above-ground support 16 for the tower leg.

Applicant has also proposed in US patent application publication 2017/0321388, published on Nov. 9, 2017 a foundation and a method of installing a foundation that uses the borehole approach, but with tension anchors that stabilize the column. In some cases, the borehole does not need to penetrate the bedrock to any significant depth.

SUMMARY

Applicant has found that it is a challenge to connect a tower leg to a column-type foundation. One issue is that the connection of the tower leg to the base (i.e. the top or cap of the column-type foundation) involves creating the attachment on site. Another issue is that the ability to drill a borehole with exact precision in position so that the center of the column-type support is centered with the tower leg is very difficult.

Applicant proposed herein to provide a position adjustable cap for a column-type foundation. Such a cap can provide a base mounting for a leg of a tower that is solidly connected to the column while being adjustable during installation in a number of axes. Such a cap can be adjusted to be in the precise position desired so that it can provide an integral attachment strap or member having one or more connection surfaces for connection to the leg of the tower.

The cap can be connected to the column using a central bar or bolt anchored in the column. Alternatives to using a central bar or bolt are possible, however, they are more complicated. For example, it is possible to use a plurality of bars or bolts extending down and anchored into the column. While potentially stronger, this can be more complicated to adjust in position. Alternatively, the cap can be attached to the main column using fasteners extending perpendicular to the lengthwise axis of the column to be supported by the casing or sleeve of the column (in the case that the column has a casing) or by the body of the column.

The cap can be fixed in its adjusted relative position with respect to the column by using a settable filling material such as cement, concrete, epoxy, resin, etc. to hold a position fixed prior to the setting of the material. The cap can provide a sealed casing for the settable filling material and the casing can be adjusted in the desired position using an external support or by using members that are part of the casing. A compliant seal can be used at the bottom of a cylindrical casing to provide sufficient tolerance for adjustment in position. Set screws can be used as members that are part of the casing to position the casing with respect to the column.

The way in which the cap held in position using a settable filling material is connected to the column can take different forms as described above. When a central bolt or bar is used, the connection between the cap and the bar can allow for setting the height of the cap while allowing for adjustment in a plane perpendicular to the lengthwise axis of the column, while allowing for adjustment of the cap in other directions using the positioning of the casing relative to the column. The settable filling material can then solidify the positioning of the cap.

Alternatively to using a settable filling material, the adjusted relative position can be set using adjustable members such as a nut and bolt or using strapping that can be secured at a desired variable position.

While the adjustable cap represents mechanical components and methods of installation related to only a small portion of the foundation, Applicant believes that it represents a key element in providing for efficient and reliable electrical power transmission. Transmission lines fail when a single tower fails. Towers are thus typically overdesigned to handle the most extreme conditions. This means that the foundations for the towers are also overdesigned. The extent of the foundation preparation when such work involves excavation leads to environmental damage in addition to significant costs. When borehole column type foundations are used, a cap that is solidly connected to the column is important and the process of drilling does not allow for precision positioning of the resulting base or cap to the placed at the top of the column.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be better understood by way of the following detailed description of certain embodiments with reference to the appended drawings, in which:

FIG. 1 is a schematic illustration of a conventional installation of a four-legged electrical power line transmission tower showing excavated pits, exposed bedrock, foundations mounted on the bedrock for supporting each leg at ground level;

FIG. 2 is a side sectional view of a borehole column type foundation in which the column is planted into the bedrock to provide a foundation support at the ground surface;

FIG. 3 is a side sectional view of a borehole column type foundation column having an adjustable cap for connecting to an angle-iron type leg of a tower according to one embodiment;

FIG. 4 is a flow chart describing the installation steps for the embodiment of FIG. 3;

FIG. 5 is an oblique, partly-break-away view of the embodiment of FIG. 3;

FIG. 6 is a side sectional view of a borehole column type foundation column installed at an angle with respect to the vertical and having an adjustable cap connected to an angle-iron type leg of a tower according to one embodiment;

FIG. 7 is a plan view of a cap according to the embodiment of FIGS. 3 and 4;

FIG. 8 is a plan view of a cap according to an embodiment in which three tension anchors are connected to the cap for stabilizing the column;

FIG. 9 is sectional side view of the anchor attachment of the embodiment of FIG. 8;

FIG. 10 is a schematic illustration of a four-legged tower mounted to borehole column type foundations of the type illustrated in FIGS. 3, 5 and 7;

FIGS. 11A-11B are schematic illustrations of a borehole column type foundation column having an adjustable cap for connecting to an angle-iron type leg of a tower according to one embodiment;

FIGS. 12A-12B are schematic illustrations of a four-legged tower mounted to borehole column type foundations of the type illustrated in FIGS. 11A-11B, and details thereof;

FIGS. 13A-13F are schematic illustrations of a method of installing a borehole column type foundation of they type illustrated in FIGS. 11A-11B;

FIG. 14 is a schematic illustration of a borehole column type foundation column having an adjustable cap for connecting to an angle-iron type leg of a tower according to one embodiment;

FIG. 15 is a schematic illustration of a four-legged tower mounted to borehole column type foundations of the type illustrated in FIG. 14; and

FIGS. 16A-16D are schematic illustrations of a four-legged tower mounted to borehole column type foundations including tension members, and details thereof.

DETAILED DESCRIPTION

In general, the present disclosure relates to electrical power transmission towers, borehole column type foundations for the towers, and adjustable caps for use in the foundations. The disclosure also relates to methods of installing the foundations, caps, and towers. As discussed above, the systems and methods disclosed herein may have advantages over the prior art and may in particular provide for efficient and reliable electrical power transmission.

In the embodiment of FIG. 3, there is shown a borehole column type foundation in which a column 12 is embedded into bedrock 3 and set in its borehole using sealant 15. The column 12 illustrated is of the type that has a hollow casing filled with concrete or cement 14, such as 30 megapascal (MPa) cement (preferably the settable material should be able to withstand more than 25 MPa and in some cases up to 40 MPa for a transmission tower application, however, this resistance to pressure can vary from the needs of the column foundation). The sealant 15 can be the same material as the filler 14 for the column and the column 12 can have apertures (not shown) for the cement 14 to pass through the column 12.

In some cases, the column 12 can comprise an H- or an I-beam (or other rigid member) that is set in a settable material such as cement or concrete 14. In such cases, it can be desirable to weld or attach bar 18 to the I-beam. In some embodiments, the column casing and sealant 16 can be replaced by the concrete surrounding the I-beam.

The column 12 in FIG. 3 is anchored in the bedrock 3 and rises up through the overburden layer 2. This involves drilling into the bedrock 3. Applicant uses a drill rig attached to a stable support and capable of drilling a borehole in a relatively straight line through soft ground and through any rocks or boulders in the overburden layer 2. The column 12 can alternatively be set on the bedrock (rather than in it) and stabilized using side anchors as described in Applicant's US patent application publication 2017/0321388, published on Nov. 9, 2017.

A cap 16 can cover the top of the column 12. The cap 16 can be solidly connected to the column 12 as the leg of the tower (or other structure to be supported) can apply not only downward forces but also upward forces as the wind acts on the tower. The cap 16 can be given most of its strength through its connection to the bar 18 that is embedded in the column material 14. The bar 18 can be textured like rebar so as to hold well in the material 14.

In the embodiment of FIG. 3, the adjustable position of the cap 16 with respect to the column 12 come from an adjustable connection between the central bar 18 and the cap 16 that is locked in place using a settable material 36 filling a casing 35 that can seal against the column 12 using a seal 24. The settable material 36 provides load resistance in at least compression, while the bar 18 provides a solid connection in tension as well. While not shown in FIG. 3, the cement 15 (or other suitable settable material) can extend between the column 12 and the overburden layer 2, namely it can fill a space between the borehole and the column 12.

The setting of the material 14 can take a few days in the case of cement. It will be understood that a holder (not shown) can be used to hold the bar 18 in place during setting or curing of the material 14. The precision of the final position of the bar 18 is very difficult to ensure during this process.

The upper end of the bar 18 can be threaded so that nuts 20 and 30 can be adjustably positioned thereon. An aperture 22 in the cap 16 allows the cap 16 to be positioned laterally within a range of movement. The cap 16 is sandwiched between plates 22 and 28 that have central holes fitting over the bar 18. The double nuts 20 and 30 allow for adjusting height and locking the position when the nuts are turned to compress against each other. In this way, the cap can be attached to the column 12 with an adjustable height and horizontal position. The cap 16 can be rotated about its vertical axis so as to position the leg support members 38 and 40 as desired. The exact leveling and position can also be set using screws 32 (three can be provided as shown in FIGS. 7 and 8).

While three threaded screws 32 can be used that are turned to adjust their position, it will be appreciated that other adjustable length members can be used in a similar manner to provide the position adjustment between the casing 35 and the top of the column 12.

It will be appreciated that the embodiment of FIG. 3 allows for a limited displacement of the cap 16 within a plane perpendicular to the lengthwise direction of the column 12, while allowing for rotation about the lengthwise direction of the column 12 as well as some adjustment in orientation of the top surface of the cap 16 using the set screws 32. In total this gives the embodiment of FIG. 3 six degrees of freedom including the ability to adjust its height using rod 18. It will be appreciated that as few as two degrees of freedom can be practical, although three or more will typically be provided.

Once the cap 16 is correctly positioned, a filling hole 34 in the cap 16 is used to fill the chamber defined by the cap 16 and its casing 35 and seal 24. The filling material can be a sealant material or cement providing suitable load resistance properties. The seal 24 can be an O-ring as illustrated, a compressible flap, a wadding material stuffed between the outside of the column 12 and the bottom of the casing 35 (this can require clearing some of the soft ground around the top of the column 12 to access the gap from below), by pouring a compactable filler, such as sand, into the cap 16 through one or more inlets 34 to fill up the bottom of the chamber to be then filled up with the settable material 36, or the soft ground surrounding the bottom of the casing 35 can be suitably compacted to be sufficiently nonporous while the settable material 36 sets in the cap 16.

It will be appreciated that the rod 18 is anchored in the column 12 to provide resistance when the leg of the tower (or of any other structure being supported) pulls up. Such traction could be greater than the resistance of the cement or other settable material 36 and cause cracking. However, it will be appreciated that there are alternatives to using a rod 18 that is anchored in the material 14 or attached to a column structural member. For example, in the case that the column's cylindrical tube is strong enough to withstand the pulling forces, the column foundation 12 does not need rod 18, and the cap 16 could be secured to the column after the material 36 is hardened by drilling two orthogonal and spaced apart holes across casing 35 and the upper end of the cylinder of the column 12. Bolts extending through the holes can then secure the cap 16 to the column 12. Alternatively, the rod 18 need not be anchored into material 14 and instead can be anchored to the upper part of the tube 12 using a bracket with radial arms that can be bolted to the tube wall of the upper end of the column 12 so as to connect the rod 18 to the side wall of the upper end of the column 12. In this way, the length of rod 18 can be shorter and does not require embedding the material 14.

FIG. 5 illustrates an oblique view of FIG. 3 with the column and cap partly cut-away.

FIG. 6 shown an installation of a foundation column 12 of the type shown in FIG. 3 at an angle to the vertical. The tower leg can be in-line with the lengthwise axis of the column 12.

FIG. 7 illustrates a top of the cap according to the embodiment of FIGS. 3 and 6. The cap 16 can be made for example of corrosion resistant steel. While the leg supports 38 and 40 illustrated are for receiving an angle iron shaped leg, it will be appreciated that other suitable supports for the structure to be supported are possible. The angle iron shaped support 38 is provided with holes for fastening the tower leg to the support 38.

FIG. 8 illustrates a cap 16 adapted for use with side anchors 45. As described in US patent application publication 2017/0321388, published on Nov. 9, 2017, a side anchor 45 is installed in a small borehole 47 and filled with a sealant 48 that can be a suitable cement. The anchor is thus supported by the length of its borehole in the overburden layer and/or by its anchoring in the bedrock. The anchor can be a rod or a cable that is placed under tension, for example using a threaded member 50. The anchor can be connected to the cap 16 at pivotable supports 52 that are received in sockets 54 of cap 16, as shown in FIG. 9. The anchors 45 pass through an opening 56 in cap 16 such that a range of angular motion is possible by pivotable supports 52 that are connected to the anchors 45. By applying sufficient tension at each anchor 45, the foundation column 12 can be stabilized at the cap 16.

It will be appreciated that when three or more tension anchors 45 are used, the column 12 can be always subject to a compression load. In this case, the use of rod 18 to provide the cap with the ability to resist an upward pulling force is not required. Thus in the embodiment of FIG. 8, the rod 18 is optional, as the cap 16 can be held in position during setting of the material 36 using the set screws 32 and/or other adjustable supports.

FIG. 10 is a schematic illustration of a tower having four legs installed on borehole column-type foundations. As shown, the lengths of the tower legs can be adjusted in accordance with the terrain such that some legs are longer than others. The length of the columns can likewise vary in accordance with the depth of the overburden layer 2.

FIGS. 11A-11B illustrate a borehole column type foundation with an adjustable cap, showing a side view cross-section, an oblique, partly-break-away view, and a top view, respectively. FIGS. 11A-11B illustrate an embodiment similar to that shown in FIGS. 3 and 5. Like elements are labelled with like reference signs, and some elements which do not differ between the embodiments may not be described here. Features described with respect to FIGS. 3 and 5 may be combined with features described here and advantages described with respect to FIGS. 3-5 may apply to the embodiments discussed here.

The advantage of the embodiment of FIGS. 11A to 11B over the embodiment of FIGS. 3 and 5 is that the adjustable cap can be set into its desired position using vertically adjustable set screws 68, for example three in number, that allow the cap to be positioned in height and inclination with respect to the column 12 using gravity to stabilize the cap 35 until the settable material is used to solidify the combination. Lateral adjustment members or screws 32 can be used to better hold the desired position of the cap until the settable material is used to solidify the combination. The use of the vertical adjustment members 68 makes the installation of the cap 35 easier.

The embodiment of FIGS. 11A to 11B also offer the option that the base 16 be a separable component from the cap 35. This allows for the base 16 to be customized and it also makes the cap lighter during its installation. The base 16 can be bolted to the top of the cap 35.

FIGS. 11A-11B show a borehole column type foundation in which a column 12 and a bar 18 are set in a pilot hole 42 and a borehole 44 formed in bedrock 3. The pilot hole 42 and the bar 18 may extend below the borehole 44 and the column 12. Both the bar 18 and the column 12 may be set using a sealant 14, 15, such as concrete. In some embodiments, the column 12 and the bar 18 may be attached to each other.

The column 12 and the rod 18 may be anchored in the bedrock 3 and rise up through the overburden layer 2. The column 12 may alternatively be set on the bedrock (rather than in it) and stabilized using side anchors as described in Applicant's US patent application publication 2017/0321388, published on Nov. 9, 2017. If the column 12 is set on the bedrock 3, the bar 18 may be set on the bedrock 3 or embedded in the bedrock 3.

A cap assembly 46 may cover the top of the column 12. The cap assembly 46 may comprise a cap 16, a casing 35, one or more screws 32, and an adjustable plate 50. The cap assembly 46 may also be connected to the bar 18. The cap assembly 46 may be configured to attach the column 12 and the bar 18 to a leg support member 38, which may support an electrical tower leg (not shown). The cap assembly 46 may thereby anchor the electrical tower leg to the borehole foundation. In some embodiments, the cap assembly 46 may be partially disposed in a hole formed in the overburden layer 2. Overburden material 2 may or may not be replaced to partially cover the cap assembly 46.

The cap 16 may cover the top of the column 12 and may be connected to it through any means known in the art. In some embodiments, the cap 6 may be rigidly connected to the column 12. The bar 18 may extend through a hole formed in the cap 16 and may or may not be attached to the cap 16.

The casing 35 may be disposed around an outer surface of the column 12 and may be connected to the column 12 via the screws 32. A seal 24 may be disposed between the column 12 and the casing 35. The screws 32 may be used to adjust the orientation of the casing 35 relative to the column 12. Namely, the specific degree to which each screw 32 is tightened may impact the orientation of the top of the casing to which the adjustable plate 50 is attached. The cap assembly 46 may include any number of screws 32. In some embodiments, the cap assembly 46 may include eight screws 32 arranged around the casing 35 in pairs, as shown in FIG. 12B. The screws 32 may be tightened to the casing 35 using nuts.

The adjustable plate 50 may be disposed on the top surface of the casing 35 above the cap 16. The bar 18 may extend through the center of the adjustable plate 50. One or more nuts 30 may be used to attach the bar 18 to the adjustable plate 50. The attachment between the bar 18 and the adjustable plate 50 may provide most of the strength of the connection between the adjustable plate 50 and the borehole foundation; the attachment may provide the strength necessary to support the electrical tower leg.

The adjustable plate 50 may comprise one or more fine adjustment screws 48. As discussed above, gross positioning of the adjustable plate 50 may be made by positioning the casing 35 using the screws 32. The screws 32 may orient the casing 35 such that the adjustable plate 50 rests on the casing 35 in a desired orientation. However, the adjustable plate 50 may not be at the precisely desired orientation. Accordingly, the fine adjustment screws 48 may be used to make fine adjustments to the orientation of the adjustable plate 50. As shown in FIG. 12B, a number of fine adjustment screws 48 may be arranged around the diameter of the adjustable plate 50. Adjusting the length of each fine adjustment screw 48 extending below the adjustable plate 50 may allow for fine adjustments to be made to the orientation of the adjustable plate 50.

In some embodiments, modeling software or another computer program may be used to determine how the screws 32 and the fine adjustment screws 48 should be adjusted to position the adjustable plate 50 at a particular angle. In some embodiments, measurement devices may be used on-site to make the adjustments.

The leg support members 38, 40 which support an electrical tower leg may be attached to the adjustable plate 50 via a leg support mount 52. The leg support mount 52 may be rigidly attached to the leg support members 38, 40 and may comprise an attachment plate 54 and a mounting base 56. The attachment plate 54 may be configured to be attached to the adjustable plate 50 via bolts 58 or through any other means known in the art. The mounting base 56 may extend from the attachment plate 54 and include a hollow central region to contain the bar 18 and nuts 30.

FIGS. 12A-12B illustrate embodiments of an electrical tower 90 supported by legs 92 mounted on borehole foundations. Each leg 92 of the electrical tower 90 may be connected to a leg support member 38, 40 supported by a borehole foundation as described above.

The leg support members 38, 40 may extend from the mounting base 56 at an angle. As shown in FIGS. 12A-12B, the leg support members 38, 40 may be in line with the legs 92 of the electrical tower. The leg support mounts 52 may be configured to be approximately parallel to the surface of the overburden layer 2. In the embodiments illustrated in FIGS. 11-12, the borehole foundations may be perpendicular to the surface of the overburden layer 2. Accordingly, the adjustable plates 50 may be adjusted to be approximately parallel to the surface of the overburden layer 2. In some embodiments, the leg support mounts 52 and the adjustable plates 50 may be at a different orientation. For example, local variations in the surface of the overburden layer 2, as shown in FIGS. 12A-12B may necessitate variations in the orientation of the adjustable plates 50.

Comparing FIGS. 11A-11B to FIGS. 3 and 5, one skilled in the art will recognize two key areas of difference: the base of the foundation and the cap/cap assembly. Namely, FIGS. 11A-11B illustrate a base which includes a rod 18 extending below a column 12 and a cap assembly featuring an adjustable plate. The foundation base illustrated in FIGS. 11A-11B may be used with the cap illustrated in FIGS. 3 and 5 and the foundation base illustrated in FIGS. 3 and 5 may be used with the cap assembly illustrated in FIGS. 11A-11B without departing from the scope of this disclosure. One skilled in the art will recognize that features from the different illustrated embodiments may be combined and modified in other ways, also without departure from the scope of the disclosure.

FIGS. 13A-13F illustrate a method of installing a borehole foundation as illustrated in FIGS. 11-12.

FIG. 13A illustrates the formation of three holes: a pilot hole 42 extending into the bedrock 3, a borehole 44 extending through the overburden layer 2 and into the bedrock 3, and a surface hole 60 formed at the surface of the overburden layer 2. The holes may be formed through drilling, excavating, or any other means known in the art. In some embodiments, these holes may be formed using techniques well known from petroleum production applications. FIG. 13B illustrates the insertion of a bar 18 into the pilot hole 42 and a column 12 into the borehole 44. FIG. 13C illustrates the filling of the pilot hole 42 and the borehole 44 with a filler 14, 15 such as cement. The region of the pilot hole 42 surrounding the bar 18 may be filled. The regions of the borehole 44 surrounding the column 12 and between the column 12 and the bar 18 may be filled. The filling may be performed using any means known in the art, including techniques well known from petroleum production applications.

FIGS. 13D-13F illustrate the installation of a cap assembly 46 on the bar 18 and column 12. A cap 16 may be disposed on top of the column 12. A casing 35 may be installed around the column 12 at a desired angle using screws 32. An adjustable plate 50 may be disposed on top of the casing 35, and the orientation of the adjustable plate 50 may be adjusted using fine adjustment screws 48. One or more nuts 30 may be used to secure the cap assembly 46 to the bar 18. A washer may or may not be disposed between the nuts 30 and the adjustable cap 50. In some embodiments, these steps may be performed with the guidance of modeling software and/or measurement tools to ensure a desired orientation of the adjustable plate 50.

FIG. 13F illustrates the installation of a leg support mount 52 and attached leg support members 38, 40. An attachment base 54 of the leg support mount 52 may be attached to the adjustable plate 50 via screws or any other means known in the art. The orientation of the adjustable plate 50, which was carefully selected and achieved as illustrated in FIGS. 13D-13E may ensure that the leg support members 38-40 are oriented correctly to support the leg of an electrical tower as illustrated in FIGS. 12A-12B.

FIGS. 14-15 illustrate an alternative to the embodiments illustrated in FIGS. 11-13. FIG. 14 illustrates a borehole foundation including the same components as those illustrated in FIGS. 11A-11B. FIG. 15 illustrates an electrical tower 90 supported by such borehole foundations. The borehole foundation illustrated in FIG. 14 is oriented at an angle to the surface of the overburden 2. In contrast to the embodiments illustrated in FIGS. 11-13, FIGS. 14-15 illustrate leg support members 38, 40 which extend perpendicular to the mounting base 56. The leg support members 38, 40 may be in line with the legs 92 of the electrical tower 90. Accordingly, the borehole foundation may be formed at an angle equal to or similar to the angle of the legs 92. Technology for drilling or otherwise forming angled boreholes is well known in the art. One skilled in the art will readily understand how to use the method of FIGS. 13A-13F to install borehole foundations at an angle.

FIGS. 16A-16D illustrate the use of side anchors 45 to secure tower legs 92 anchored to borehole foundations. FIG. 16A illustrates an electrical tower 90 with four legs 90, each leg being attached to a borehole foundation. FIG. 16B illustrates detail of a cap assembly 46, a leg support mount 52, and leg supports 38, 40 illustrated in FIG. 16A. FIGS. 16C-16D show cross sections of FIGS. 16A and 16B, respectively.

As discussed above, it will be appreciated that when three or more tension anchors 45 are secured to a borehole foundation, the column 12 of the borehole foundation can be always subject to a compression load. The compression load provides for a strong foundation. As shown in FIG. 16A, each foundation/leg 92 is secured by one external tension anchor 45, which is connected to the ground, and two inter-leg tension anchor 45, which is secured to another foundation/leg 92. The inter-leg tension anchors 45 are illustrated as being connected between neighboring legs 92 but could be connected in a different pattern.

The leg support mount 52 shown may be adapted similarly to the cap illustrated in FIG. 8. Specifically, the leg support mount may include extensions which provide for the attachment of side anchors 45. In some embodiments, the leg support mount 52 may include one external mount 62 for an external tension anchor 45 and two inter-leg mounts 64 for inter-leg tension anchors 45. The external mount 62 may comprise an extension angled upward with a hole formed therethrough, such that it supports an external tension member 45 which extends at an outward angle from the foundation. The tension member 45 may be connected through the hole with one or more nuts or through any other means known in the art. In some embodiments, the external tension member 45 and the external mount 62 may be connected via a rotatable/pivotable connection as illustrated in FIGS. 8 and 9.

The inter-leg mounts 64 may comprise vertical extensions with holes formed therethrough, such that the tension members 45 may be attached thereto via a pivot attachment or any other means known in the art. A leg support mount 52 may include extensions/mounts which differ from those illustrated in FIGS. 16A-16D. One skilled in the art will readily envision different ways in which a tension anchor 45 may be attached to a leg support mount 52.

The inter-leg tension members 45 may include tensioning mechanisms 66, which may allow them to be tightened/loosened after they have been attached to two legs 92. These mechanisms 66 may operate via a screw or any other means known in the art and may allow a desired amount of tension to be applied to the borehole foundations and the legs 92 they support. Each of the external tension members 45 may be secured in a borehole. The borehole may be angled and the external tension member 45 may be cemented into the borehole. The borehole may extend into the bedrock.

The configuration of tension members 45 shown in FIGS. 16A-16D may provide several advantages. As discussed above, connecting three tension members 45 to each leg/borehole foundation allows each of the legs/foundations to be maintained in tension at all times. By connecting two inter-leg tension members 45 to each leg, the configuration reduces the number of tension members 45 which must be installed, and in particular, reduces the number of external tension members 45 which must be secured to the ground. This reduces the number of boreholes which must be formed in the overburden and the bedrock, thereby reducing the time and cost necessary to install tension members. Further, by having numerous tension members accessible above-ground, this configuration may allow for adjustments to be made more readily after the tension members have been installed. 

What is claimed is:
 1. A method of installing a foundation comprising: drilling a borehole; providing a column structure in said borehole; filling at least a space between said borehole and said column structure with a first settable material; hardening said first settable material wherein said column structure combined with said first settable material forms a foundation column; providing a cap having a top structure-engaging surface; supporting said cap while adjusting a position of said cap with respect to said foundation column with at least two degrees of freedom; providing a second settable material between said foundation column and said cap while maintaining said position; hardening said second settable material to make said cap structurally integral with said foundation column with said cap secured in said position.
 2. The method as defined in claim 1, wherein said drilling said borehole comprises drilling through an overburden layer into a bedrock layer, said foundation column deriving lateral stability from said bedrock layer.
 3. The method as defined in claim 1, wherein said foundation column comprises a bar extending upwardly for attaching said cap.
 4. The method as defined in claim 3, wherein said supporting said cap comprises fastening said cap to bar at a desired height.
 5. The method as defined in claim 3, wherein said providing said second settable material between said foundation column and said cap comprise providing a container between said foundation column and a bottom of said top structure engaging surface for containing said second settable material.
 6. The method as defined in claim 1, wherein said column structure is a cylindrical member.
 7. The method as defined in claim 6, wherein said column structure is a cylindrical tube and filled with said first settable material.
 8. The method as defined in claim 1, wherein said first settable material and said second settable material are cement.
 9. The method as defined in claim 1, wherein said supporting said cap while adjusting a position of said cap with respect to said foundation column with at least two degrees of freedom comprises using adjustment screws extending from said cap to said foundation column.
 10. The method as defined in claim 9, wherein said adjustment screws include vertical adjustment screws extending between a horizontal member of said cap and a horizontal member of said foundation column.
 11. A method of installing a tower comprising: providing the tower having at least one leg; defining a position and orientation for said at least one leg; installing at least one foundation in accordance with claim 1, wherein said position of said cap corresponds to said position and orientation for said at least one leg; securing said at least one leg to said cap.
 12. The method as defined in claim 11, wherein said tower comprises four legs, said installing comprising installing four said foundations.
 13. The method of claim 11, further comprising connecting three tension members to each foundation and applying tension to the foundation via the tension members.
 14. The method of claim 12, further comprising connecting at least one tension member between two foundations.
 15. The method of claim 12, further comprising connecting four tension members between the four foundations, such that two of the four tension members are connected to each of the four foundations.
 16. The method of claim 15, further comprising connecting a tension member from a foundation to a substrate proximate the foundation.
 17. The method of claim 16, wherein the substrate comprises a bedrock.
 18. A cap for a column-type foundation comprising: a top member having a support member for mating with and securing a leg of a structure; a central aperture for receiving an anchor rod of said column-type foundation; a sidewall casing extending downwardly from said top member; at least three positioning members for engaging said column-type foundation; a seal located on an inside of the sidewall casing near a bottom of the sidewall casing; and aperture for filling the cap with a settable material when connected to a column-type foundation.
 19. The cap as defined in claim 18, wherein said position members include positioning members mounted in the sidewall casing to be adjustable in position extending into the sidewall casing.
 20. The cap as defined in claim 18, wherein said position members include positioning members mounted in said top member for engaging a top member of said column-type foundation to provide for vertical adjustment and leveling.
 21. The cap as defined in claim 20, wherein said top member comprises a cover plate connected to said sidewall casing and a base member fastenable to said cover plate.
 22. A cap for a column-type foundation comprising: a top member connectable to a top of the column-type foundation; and at least three pivotable anchor attachments seated in said top member. 